Package-on-package process for applying molding compound

ABSTRACT

A method of packaging includes placing a package component over a release film, wherein solder balls on a surface of the package component are in physical contact with the release film. Next, A molding compound filled between the release film and the package component is cured, wherein during the step of curing, the solder balls remain in physical contact with the release film.

BACKGROUND

In a conventional package-on-package (POP) process, a top package, inwhich a first device die is bonded, is further bonded to a bottompackage. The bottom package may also be bonded with a second device die.As a result, the second device die may be on the same side of the bottompackage as the solder balls that are used to bond the bottom package tothe top package.

Before the bonding of the top package to the bottom package, a moldingcompound is applied on the bottom package, with the molding compoundcovering the second device die and the solder balls. Since solder ballsare buried in the molding compound, a laser ablation or drilling isperformed to form holes in the molding compound, so that the solderballs are exposed. The top package and the bottom package may then bebonded through the solder balls in the bottom package.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1 through 4 are cross-sectional views of intermediate stages inthe formation of a top package in accordance with an embodiment;

FIGS. 5 through 7 are cross-sectional views of intermediate stages inthe formation of a bottom package in accordance with an embodiment,wherein a compressive molding method is used to apply a moldingcompound;

FIGS. 8 and 9 illustrate the bonding of the top package to the bottompackage; and

FIGS. 10 and 11 are cross-sectional views of intermediate stages in theformation of a bottom package in accordance with an alternativeembodiment, wherein a transfer molding method is used to apply a moldingcompound.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

A package-on-package (PoP) bonding method and the resulting packagestructure are provided in accordance with various embodiments. Theintermediate stages of manufacturing a package structure in accordancewith an embodiment are illustrated. The variations of the embodimentsare then discussed. Throughout the various views and illustrativeembodiments, like reference numbers are used to designate like elements.

Referring to FIG. 1, package component 10 is provided. Package component10 may comprise substrate 11 that is formed of a semiconductor material,such as silicon, silicon germanium, silicon carbide, gallium arsenide,or other commonly used semiconductor materials. Alternatively, substrate11 is formed of a dielectric material. Package component 10 isconfigured to electrically couple metal bumps 12 on first surface 10A tometal features such as bond pads 16 on second surface 10B opposite firstsurface 10A. Accordingly, package component 10 may include metallines/vias 14 therein. In an embodiment, package component 10 is aninterposer. In alternative embodiments, package component 10 is apackage substrate.

Die 20 is bonded to package component 10 through metal bumps 12. Metalbumps 12 may be solder bumps or other types of metallic metal bumps.Throughout the description, metal bumps 12 are alternatively referred toas solder bumps 12. Die 20 may be a device die comprising integratedcircuit devices, such as transistors, capacitors, inductors, resistors(not shown), and the like, therein. Furthermore, die 20 may be a logicdie comprising core circuits, and may be, for example, a centercomputing unit (CPU) die, or a memory die. The bonding between die 20and metal bumps 12 may be a solder bonding or a direct metal-to-metal(such as a copper-to-copper) bonding. An underfill (not shown) may bedispensed into the gaps between die 20 and package component 10.

Referring to FIG. 2, molding compound 24 is molded onto die 20 andpackage component 10 using, for example, compressive molding or transfermolding. Accordingly, die 20 is protected by molding compound 24. InFIG. 3, solder balls 26 are mounted on bond pads 16 on surface 10B ofpackage component 10. Solder balls 26 and die 20 may be on oppositesides of package component 10. A reflow is performed on solder balls 26.Top package 30 is thus formed. Next, as shown in FIG. 4, a flux dippingis performed to apply flux/solder paste 28 onto solder balls 26.

Referring to FIG. 5, bottom package 40 is formed. Bottom package 40includes package component 42, which may be an interposer, a packagesubstrate, or the like. Package component 42 is configured toelectrically couple solder balls 44 and/or metal bumps 45 at the topsurface to bond pads 43, which is at a bottom surface of packagecomponent 42. The metal connections from metal bumps 45 to solder balls44 and/or bond pads 43 are not shown, although they may also exist.Furthermore, package component 42 may include metal lines and vias, bothshown as 46, therein.

Die 50 is bonded to package component 42 through metal bumps 45. Metalbumps 45 may be solder bumps or other types of metallic metal bumps. Die50 may be a device die such as a logic die or a memory die. The bondingbetween die 50 and bumps 45 may be a solder bonding or a directmetal-to-metal (such as a copper-to-copper) bonding. An underfill (notshown) may be dispensed into the gaps between die 50 and packagecomponent 42. Solder balls 44 may be mounted on the same side of packagecomponent 42 as die 50. Solder balls 44 have great sizes, so that thetop ends 44A of solder balls 44 may be higher than top surface 50A ofdie 50.

FIGS. 6 and 7 illustrate the cross-sectional views of intermediatestages in a compressive molding to apply molding compound 66 on package40. Molding compound 66 may be a resin or other types of dielectricencapsulating material. Referring to FIG. 6, a part of mould 62, whichis part of compressive molding apparatus, is illustrated. Mould 62 isconfigured to be heated to desirable temperatures. Cavity 64 is formedin mould 62. Movable compression block 63 is under cavity 64, and isconfigured to be moved up and down, as symbolized by the arrows, so thatthe depth of cavity 64 may be changed.

Release film 60 is placed on mould 62, and extends into cavity 64.Release film 60 is relatively soft, so that when solder balls arepressed into it, the solder balls are not damaged, and the solder ballsmay substantially maintain their shapes. Release film 60 may be afluorine-base film, a silicon-coated polyethylene terephthalate film, apolymethylpentene film, a polypropylene film, or the like. Mould 62 maycomprise small holes (not shown), so that when vacuumed, release film 60may have good contact with movable compression block 63, the sidewallsof mould 62 (in cavity 64), and the top surfaces of mould 62.Accordingly, substantially no air bubble is formed between release film60 and mould 62, and between release film 60 and movable compressionblock 63. Release film 60 also forms a cavity, which is also shown ascavity 64. Molding compound 66, which is in a liquid form, is placed incavity 64 and over release film 60. Bottom package 40 is then placedover cavity 64, with die 50 and solder balls 44 facing cavity 64.

Referring to FIG. 7, device die 50 and solder balls 44 are placed intocavity 64. Movable compression block 63 may also be pushed upwardly, sothat molding compound 66 is pushed up to fill in the spaces betweensolder balls 44, and fill in the space between die 50 and solder balls44. Molding compound 66 may also be in physical contact with surface 42Aof package component 42. The amount of molding compound and therespective thickness T1 (FIG. 6) is controlled, so that solder balls 44penetrate through molding compound 66, with solder balls 44 at least inphysical contact with release film 60. In an embodiment, solder balls 44are pressed against release film 60, with a first portion of each ofsolder balls 44 pressed into release film 60. A second portion of eachof solder balls 44 is not pressed into release film, so that they areinside and in contact with molding compound 66. As shown in FIG. 6,depth T1 of molding compound 66 pre-placed in cavity 64 may be smallerthan height H3 of solder balls 44. Die 50, on the other hand, may, ormay not, be in physical contact with release film 60. In FIG. 7, lines50′are drawn to mark the left side, the right side, and the bottom sideof die 50′when the bottom side is in contact with release film 60. In anembodiment, die 50 does not penetrate into release film 60.

Molding compound 66 is then cured, for example, by heating mould 62.During the curing step, solder balls 44 remain in physical contact withrelease film 60, and solder balls 44 may also remain to be pressed intorelease film 60. After the heating to cure molding compound 66, bottompackage 40 is separated from release film 60. The resulting bottompackage 40 is illustrated in FIG. 8.

As shown in FIG. 8, the portions of solder balls 44 that are in contactwith, and possibly pressed into, release film 60 when the curing isperformed do not have molding compound 66 thereon. The cured moldingcompound 66 has top surface 66A, which may be substantially flat. Topends 44A of solder balls 44 may be at least level with, and may behigher than, top surfaces 66A. Accordingly, all solder balls 44 areexposed through cured molding compound 66. Die 50 may be buried under athin layer of molding compound 66. Alternatively, die 50 may be exposedand having a top surface level with top surface 66A of molding compound66. Accordingly, during the molding step as shown in FIG.7, the topsurface (which is the bottom surface in FIG.7) is in contact withrelease film 60. Since release film 60 is soft, pressing solder balls 44will not cause significant change in the shape of solder balls 44, andthe shape of the exposed portions of solder balls 44 may remain to besubstantially rounded.

As also shown in FIG. 8, top package 30 as formed in the step shown inFIG. 4 is placed over bottom package 40. Since the compression moldingin accordance with embodiments results in solder balls 44 to be exposedalready, there is no need to performing a laser ablation or drilling toexpose solder balls 44 from molding compound 66. Next, as shown in FIG.9, solder balls 26 in top package 30 (please refer to FIG. 8) are placedagainst, and in contact with corresponding solder balls 44. A reflow isperformed, so that solder balls 44 and 26 are melted to form combinedsolder bumps (denoted as 26/44).

FIGS. 10 and 11 illustrate the molding of molding compound 66 to packagecomponent 42 in accordance with alternative embodiments, in whichmolding compound 66 is molded onto package component 42 through transfermolding. Unless specified otherwise, the reference numerals in theseembodiments represent like elements in the embodiments illustrated inFIGS. 1 through 9. The initial steps of this embodiment are essentiallythe same as shown in FIGS. 1 through 5. Next, as shown in FIG. 10,bottom package component 42 is placed on lower chassis 70 of a transfermolding equipment. Solder balls 44 face up. Release film 60 is placedover and in contact with solder balls 44. Upper chassis 72 is used tosuck up and hold release film 60, which forms cavity 64. Cavity 64 maybe essentially the same as cavity 64 in FIG. 6, except cavity 64 facesdownwardly in FIG. 10. Solder balls 44 are pressed against release film60, and a portion of each of solder balls 44 may be pressed into releasefilm 60. The portions of solder balls 44 pressed into release film 60have height H1. Die 50, on the other hand, may, or may not, be inphysical contact with release film 60.

Next, as shown in FIG. 11, the air in cavity 64 is vacuumed. Moldingcompound 66 is then injected into cavity 64 using plunger 74, andmolding compound 66 fills the spaces between package component 42,solder balls 44, die 50, and release film 60. A heating is thenperformed, so that molding compound 66 is cured. Bottom package 40,which now comprises molding compound 66 thereon, is then separated fromrelease film 60. The resulting package 40 is essentially the same asshown in FIG. 8. The steps as shown in FIGS. 8 and 9 may then beperformed to finish the packaging of packages 30 and 40.

By using the embodiments, after molding compound 66 is molded on packagecomponent 42, solder balls 44 are already exposed through moldingcompound 66. Accordingly, the step of laser ablation or drilling issaved. The manufacturing cost is reduced, and the manufacturingthroughput is enhanced.

In accordance with embodiments, a method of packaging includes placing apackage component over a release film, wherein solder balls on a surfaceof the package component are in physical contact with the release film.Next, A molding compound filled between the release film and the packagecomponent is cured, wherein during the step of curing, the solder ballsremain in physical contact with the release film.

In accordance with other embodiments, a method includes providing abottom package including a package component, a solder ball mounted overa top surface of a package component, and a device die over and bondedto the top surface of the package component. The solder ball has a topend higher than a top surface of the device die. The package componentis pressed against a release film, so that a first portion of the solderball is pressed into the release film, and a second portion of thesolder ball is outside the release film. The release film forms acavity, with the solder ball being in the cavity. A molding compound isfilled into the cavity. The molding compound in the cavity is cured,wherein during the step of curing, the first portion of the solder ballremains inside the release film.

In accordance with yet other embodiments, a package includes a packagecomponent, a plurality of solder balls over and mounted onto a surfaceof the package component, and a molding compound over the surface of thepackage component. Portions of the molding compound between theplurality of solder balls have top surfaces that are lower than top endsof the plurality of solder balls.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method comprising: providing a packagecomponent comprising: a device die; and solder balls, wherein the devicedie and the solder balls are at a same side of the package component;placing a release film on a mould, wherein a portion of the release filmforms a cavity; filling a molding compound in a space between therelease film and the package component, wherein the molding compound isfilled into the cavity; after the filling the molding compound, pressingthe package component against the release film, wherein first portionsof the solder balls are pressed into, and penetrate into a portion of,the release film, and second portions of the solder balls and the devicedie are not pressed into the release film, and the device die issubmerged in the molding compound; and curing the molding compound. 2.The method of claim 1, wherein during the step of curing, the solderballs remain in physical contact with the release film.
 3. The method ofclaim 1, wherein after the step of pressing, the device die does notcontact the release film, and wherein the device die is separated fromthe release film by the molding compound.
 4. The method of claim 1,wherein the step of pressing the package component is performed beforethe step of filling the molding compound.
 5. The method of claim 1,wherein the device die is bonded on the package component throughadditional solder balls that have sizes smaller than the solder balls.6. The method of claim 1 further comprising: after the step of curing,separating the package component and the molding compound from therelease film.
 7. A method comprising: providing a first packagecomprising: a first package component; a first device die bonded to asurface of the package component; and a first solder ball over thesurface of the first package component adjacent to the first device die, wherein the first solder ball has a top end higher than a top surfaceof the first device die; placing a release film on a mould, wherein therelease film forms a cavity; filling a molding compound into the cavity;placing the first package onto the molding compound by facing the firstsolder ball and the first device die toward the cavity; and pressing thepackage component against the release film, so that a top portion of thefirst solder ball is pressed into the release film, and the first devicedie is separated from the release film by the molding compound.
 8. Themethod of claim 7 further comprising: after the step of pressing, curingthe molding compound, wherein the top portion of the first solder ballremains inside the release film during curing.
 9. The method of claim 7,wherein the step of providing the first package comprises bonding thefirst device die on the surface of the first package component byforming metal bumps.
 10. The method of claim 7 further comprising: afterthe step of curing, separating the first package and the moldingcompound from the release film.
 11. The method of claim 10 furthercomprising, after the step of separating, bonding a second package tothe first package through the solder ball.
 12. The method of claim 11,wherein the second package comprises: a second package component havinga first surface and a second surface opposite to the first surface; asecond device die bonded to the first surface of the second packagecomponent; and a second solder ball over the second surface of thesecond package component, wherein the first solder ball has a top endhigher than a top surface of the first device die.
 13. The method ofclaim 12, wherein the second solder ball of the second package is bondedto the first solder ball of the first package.
 14. A method comprising:bonding a device die to a surface of a package substrate to form abottom package; mounting solder balls onto the surface of the packagesubstrate; placing a release film over a mould, wherein the release filmextends into a cavity of the mould to contact a bottom and sidewalls ofthe mould; dispensing a molding compound at the bottom of the cavity andover the release film; after the dispensing the molding compound,placing the solder balls into the molding compound; pressing the solderballs against the release film, wherein first portions of the solderballs are pressed into the release film, and second portions of thesolder balls and the device die are not pressed into the release film;and curing the molding compound.
 15. The method of claim 14, wherein thepressing the solder balls against the release film comprises pushing amovable compression block of the mould against the solder balls.
 16. Themethod of claim 14, wherein after the curing the molding compound, anentirety of the device die is molded in the molding compound.
 17. Themethod of claim 14 further comprising, after the step of curing, bondinga top package to the bottom package through the solder balls.
 18. Themethod of claim 14, wherein heights of the solder balls are greater thana thickness of the device die.